Comment on Remember When Scholastic Was Awesome? by Monkey-Scientist

Hey man guess what? You're not alone! I also know about these and though I haven't read most of them, I do own most or all. And yes I agree, though in school I was rarely allowed by my parents to order any books, I do remember how excited I used to be to look through the Scholastic (and even Arrow) catalogs at potential books of interest.

Help! I'm Trapped in My Sister's Body was the first one I found, don't remember when or how long ago, read it and really enjoyed it. Sometime afterwards, I decided to collect what others I could in this series, even though most don't have a TG or even human swap theme to them. Also imo, Todd Strasser is a good writer.

Here's what I know of/own of the rest, and it seems like I own 2 different cover versions of one of them, so there might actually have been a reprint, you might want to check it out.

Help! I'm Trapped in Obedience School
Help! I'm Trapped in Obedience School Again (only one that had a same-type-swap-sequel?)
Help! I'm Trapped in My Lunch Lady's Body
Help! I'm Trapped in an Alien's Body (the one you made this post about)
Help! I'm Trapped in the First Day of School
Help! I'm Trapped in My Gym Teacher's Body
Help! I'm Trapped in My Teacher's Body (This is the one I seem to have the 2 copies of. The full-grown teacher has his back to us and is looking in the mirror, where Jake is shown, in his own size, dressed in the teacher's brown suit, tie and glasses. A girl, must be one of Jake's Friends, is looking at the teacher with her hands on her cheeks and her mouth open in shock. Copyright 1993.)
Help! I'm Trapped in My Teacher's Body! (This is the reprint, story originally copyright 1993, reprint edition copyright 2005. This one has an ! at the end of the title, which I've not seen otherwise in this series. On the cover, we only see young Jake, facing us and a blackboard behind him, dressed as described in the mirror of the other My Teacher's Body description I gave.)

I don't know if you knew about these already, but here's a couple great recommendations you should look into. They don't have the body swap theme but they're very good still, and were also done by Scholastic.
Half Magic by Edward Eager
Seven-Day Magic (also by Edward Eager, this one is a sequel)

I'll give you an idea about the first one, without any spoilers. These are about a group of 4 kids, 2 boys and 2 girls. In the first book, they find a magic coin that has a surprising effect, not only is it magic and can grant their wishes, they have to be careful because it will only grant half of their wish, or if they wanted all of their wish, they'd have to double the effects themselves. I have yet to read all of the 2nd book but I understand it is also related to wishing, but this time the wishes last 7 days.